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Engines and parts required

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Paul james 822/10/2017 13:57:22
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Posted by Richard Wills 2 on 22/10/2017 12:55:22:

You can have the head as long as you cover postage, it is one I got in a job lot, looks good but i'll never need it. The 52 has been in storage for a while, i want to get it down and give it a run to make sure it's still good, then i'll get back to you. Planning to do that as soon as weather calms down a bit, maybe tomorrow.

Thanks Richard, if you don't want to mess about with the 52 I'll strip it and replace the bearings anyway if I have it, not usually much goes wrong with those.

Deffo up for the head, that is a very generous offer! thumbs up

Paul james 823/10/2017 22:43:52
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Had a bit of spare time today so cleaned up all the parts for the OS91FS and put it back together ready for "recapitating"

Then had a couple of hours turning up some domed aluminium prop nuts for the Flair Scouts.

Paul james 830/10/2017 09:42:07
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64 forum posts
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A friend from the local flying club came up with an old Irvine carburetor so i machined up a new inlet spigot and adapted the carb to fit the Laser 75. I put 2 O rings in the part that fits inside the head as the later ones I've seen seem to have that.

Hopefully get it running today and perhaps get a bit of video.

laser carb 1.jpg

laser carb 2.jpg

Paul james 831/10/2017 16:19:23
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64 forum posts
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 Here is the Laser 75 on the first test run after fitting the new carburetor. Sounds pretty sweet to me 

Edited By Paul james 8 on 31/10/2017 16:20:14

Edited By Paul james 8 on 31/10/2017 16:22:06

TartanMac31/10/2017 19:02:34
121 forum posts
96 photos

Hard to tell but looks and sounds like it has good compression sounds very crisp also. You done a nice job of that engine. Thanks for putting up the video did it start up easy ?

Paul james 831/10/2017 20:31:21
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64 forum posts
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Posted by TartanMac on 31/10/2017 19:02:34:

Hard to tell but looks and sounds like it has good compression sounds very crisp also. You done a nice job of that engine. Thanks for putting up the video did it start up easy ?

I do like tinkering with old engines, this one was discarded as it was very lumpy and stiff, I had a good idea it would be corroded bearings so stripped it down and sure enough it was so I replaced all 3. It didn't have either of the needles for the original Super Tigre carb so I made up an inlet spigot and adapted an old Irvine one.

Given that it had never run on that carb before it started up very easily. I set the low end screw by putting a pipe on the fuel nipple and blowing down it with the barrel slightly above the fully closed position and adjusted the screw until I could hear air hissing out. I then primed the engine and gave it a spin up on the starter, it fired right off but died so I gradually richened up the high end until it kept running.

Big thanks to Jon at Laser for the info he supplied for this old engine!

Paul james 811/11/2017 10:20:41
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64 forum posts
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Posted by Paul james 8 on 23/10/2017 22:43:52:

Had a bit of spare time today so cleaned up all the parts for the OS91FS and put it back together ready for "recapitating"

Then had a couple of hours turning up some domed aluminium prop nuts for the Flair Scouts.

Richard kindly sent me the replacement head for the OS91FS Surpass and it fitted straight on the reassembled engine.

Only problem was the intake manifold as the engine must be a MKII whereas the replacement head a MKI which had different mounting holes for the manifold on the head; the older ones has the two holes horizontally opposed whereas the MKII has them at an angle.

Now looking for an intake manifold from a MK1 OS 91 FS Surpass if anyone has one, could be the sort of part that doesn't get mashed when an engine takes a hard impact?.

Bit of a long shot but I've not been able to find one anywhere online and would like to finish the rebuild if possible.

Either that or a MKII cylinder head would sort it.

Jon Harper - Laser Engines11/11/2017 10:30:42
3087 forum posts
129 photos

I missed the progression of your laser 75, she sounds sweet

Paul james 811/11/2017 10:51:05
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64 forum posts
8 photos
Posted by Jon Harper - Laser Engines on 11/11/2017 10:30:42:

I missed the progression of your laser 75, she sounds sweet

I did wonder and was about to send you the link to the video Jon.

The Laser seems to transition very smoothly and tick over slowly, didn't take long to get to that with the newly adapted carb!.

Thanks again for your help.

Percy Verance11/11/2017 11:05:44
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5661 forum posts
108 photos

Smooth transition/linear throttling is very much a Laser strength Paul, along with that steady tickover. Quite different from the Jap and Asian four strokes, which tend to lean towards revs/top-end power.......

Jon Harper - Laser Engines11/11/2017 11:27:44
3087 forum posts
129 photos

no problem paul, you have done a great job with it. Now you have a reliable carb the engine should run for years as you have the last of the 75's with the fully hardened valve gear and clips holding carb and exhaust. Its probably got a chrome liner too and they tend to last a while.

Don Fry11/11/2017 11:41:04
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1814 forum posts
25 photos

I've got a intake for a , I think, mk 1 70, with holes horizontal. I assume it's too small?

Don Fry11/11/2017 19:03:59
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1814 forum posts
25 photos

So I have established with Paul James that my intake manifold will not fit. Mine is a low mileage mk1 70. It needs a new carb, crankcase. Anyone got one, seized? Outside chance.

Paul james 811/11/2017 19:09:10
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64 forum posts
8 photos
Posted by Don Fry on 11/11/2017 19:03:59:

So I have established with Paul James that my intake manifold will not fit. Mine is a low mileage mk1 70. It needs a new carb, crankcase. Anyone got one, seized? Outside chance.

Pity it wouldn't fit, You can see from the photo below what I mean about the kink in the inlet manifold on this model.

Somewhat oddly OS gave the same part number to the intake manifold on the MK1 and MK2 91 Surpass despite them being totally different.

back of os 91fs surpass mk1.jpg

Paul james 811/11/2017 19:53:13
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64 forum posts
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Just realised that I'm being a total Wally!! The head I have fitted will only work with the other version of the engine as that has an offset from centre carb with a straight vertical manifold.

DOH!!!

So still looking for a spare cylinder head to fit the OS91 MK2 Surpass if anyone has a busted up engine with an undamaged head.

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